The present invention relates to a method of embedding information such as copy control information and copyright information into a content such as a static picture or a moving picture as well as relates to an apparatus adopting the method.
In recent years, a content such as a picture and music is digitalized and distributed by means of storage media or a network. In order to protect the copyright of such a digitalized content, a digital-watermark technology has been regarded as an important technology.
To put the digital-watermark technology to practical use, it is necessary to optimize a content's portion to be changed, the degree of content changes or a change intensity in accordance with properties of the content. In the case of a picture, in general, in an area where condition variations of the picture are flat, if improper changes are added to pixel values such as luminance or a color-condition value, unnaturalness looks conspicuous at a changed portion. On the other hand, a picture exhibits a property referred to as a static-picture property, in accordance with which, relatively large changes added to pixels at the picture's portion with large variations in pixel value will not appear conspicuous to the eyes of a human being. An example of such a portion is an edge of the picture. In addition, a picture has a property known as a moving-picture property, in accordance with which, a static portion is sensitive to a noise while a moving portion is insensitive to noises.
Furthermore, targets of embedment of a digital watermark are not limited to a static picture. That is to say, a moving picture can also serve as a target of embedment of a digital watermark as well. A moving picture comprises a plurality of static-picture frames arranged along the time axis. It is to be noted that, during a process to appreciate the moving picture, each of the static-picture frames is appreciated as a static picture in some cases by stopping an operation to feed the frames. For this reason, in a process to embed a digital watermark into a moving picture, it is necessary to make a location of a change in pixel value inconspicuous be the location in a static-picture state or a moving-picture state. In addition, it is desirable to optimize changed pixels and the degree of the change by taking both the static-picture property and the moving-picture property into consideration.
Japanese Patent Laid-open No. 2000-175019 is an example of a document describing a method of embedding a digital watermark into a target by taking both the static-picture property and the moving-picture property into consideration. To be more specific, Japanese Patent Laid-open No. 2000-175019 describes a method of carrying out a process to make changes to luminance of a moving picture as digital watermark information when embedding the digital watermark information into the moving picture, which comprises a plurality of static-picture frames arranged along the time axis. The method comprises the steps of detecting a motion vector (a moving-picture property) for each picture block in a frame of interest, selecting a specification rule of a pixel change rate for each block in accordance with the motion quantity and selecting a number of pixels specified by the specification rule among allowable-luminance-change pixels determined by a state (a static-picture property) of each picture block.
In addition, most moving pictures are pictures compressed by typically adoption of an MPEG technique implemented by hardware or software.
In a conventional apparatus for embedding a digital watermark into a picture and compressing the picture, however, in spite of the fact that a computation of a moving-picture or static-picture property used in a process to embed the digital watermark into a picture is made the same as a computation of a moving-picture or static-picture property used in a process to compress the picture for the purpose of distinguishing a portion showing a conspicuous picture-quality deterioration and a portion showing no conspicuous picture-quality deterioration from each other, the computations are carried out separately from each other. Thus, the total processing cost of the apparatus increases, resulting a hindrance to efforts to raise the speed, reduce the size and lower the price.
In order to solve this problem, in accordance with a method disclosed in “Moving-Picture Watermarking for MPEG Encoders Sustaining Picture Qualities by Detection of Motions” written by Anzai and four other authors, the Institute of Image Information and Television Engineers' Technical Report published by the Institute of Image Information and Television Engineers, July 2002, Vol. 26, No. 48, ISSN 1342-6893, P1-6, a result of a process to search for a motion vector, which is a moving-picture property of a content (or a picture), is shared by a process to embed a digital watermark into the picture and a process to compress the picture in an attempt to reduce the processing cost.